Hydraulic versus air

[ns_in_tex]

Can I replace a air cylinder with a hydraulic cylinder?

If so, What might be any possible problems?

Thanks

 

[oldnslo]

Yes you can use hydraulic cylinders in pneumatic application. One concern can be rust since most pneumatic cylinders are made from rust resistant materials.

 

[3Ts]

Yes you can use hydraulic cylinders in pneumatic application. One concern can be rust since most pneumatic cylinders are made from rust resistant materials.

Isn't the answer more like a "yes, but". It is my understanding that the hydraulic oil is not compressible meaning whatever volume the pump puts out can be directly related to cylinder movement without regard to load. In the case of air, it is compressible so that whatever the volume of air the pump puts out does not directly relate to cylinder movement but has to include the weight (or force) to figure out how much the cylinder moves. A benefit to the air is that it acts like a shock absorber or a spring as well.

 

[jeff9366]

Can I replace a air cylinder with a hydraulic cylinder?

In what tractor application? No compact tractor that I am familiar with has an air cylinder. Compact tractor cylinders are all hydraulically operated.

 

[KennyG]

Are we talking about putting a hydraulic cylinder in place of an existing air cylinder and using it as an air cylinder? Should work but I'm not sure why you would do this. You might end up with some leakage problems because of lack of seal lubrication because the designs are different. As noted air and hydraulic systems have different characteristics because of compressiblity which is why air systems require pressurized receivers for storage while hydraulic systems run directly off the pump.

 

[ns_in_tex]

Are we talking about putting a hydraulic cylinder in place of an existing air cylinder and using it as an air cylinder? Should work but I'm not sure why you would do this. You might end up with some leakage problems because of lack of seal lubrication because the designs are different. As noted air and hydraulic systems have different characteristics because of compressiblity which is why air systems require pressurized receivers for storage while hydraulic systems run directly off the pump.

My application is, we have a foot operated sheet metal shear that was converted to operate with an air cylinder. Sometimes it needs more power and we have to use a lever bar to help it along. Thought we might have a larger hydraulic cylinder to replace it with, and still use the air for power supply.

 

[aczlan]

My application is, we have a foot operated sheet metal shear that was converted to operate with an air cylinder. Sometimes it needs more power and we have to use a lever bar to help it along. Thought we might have a larger hydraulic cylinder to replace it with, and still use the air for power supply.

That should work, you will want to include an oiler on the feed line to make sure it gets enough lubrication on the cylinder walls and to counteract the moisture in the air to reduce rust.
You might check Surplus Center to see if they carry an air cylinder in the size you need, they may have one for surprisingly cheap.

Aaron Z

 

[Norm W]

Just be careful that you don't "Over Power" the shear. We had one that a 300+lbs fellow jumped on the treadle. Broke the casting right off.

 

[3Ts]

My application is, we have a foot operated sheet metal shear that was converted to operate with an air cylinder. Sometimes it needs more power and we have to use a lever bar to help it along. Thought we might have a larger hydraulic cylinder to replace it with, and still use the air for power supply.

Before you go with a hydraulic cylinder, I'd look at either a bigger air cylinder or adding a second air cylinder. Assuming the shear isn't overpowered.

 

[aczlan]

My application is, we have a foot operated sheet metal shear that was converted to operate with an air cylinder. Sometimes it needs more power and we have to use a lever bar to help it along. Thought we might have a larger hydraulic cylinder to replace it with, and still use the air for power supply.

Before you go with a hydraulic cylinder, I'd look at either a bigger air cylinder or adding a second air cylinder. Assuming the shear isn't overpowered.

Might want to re-read the bolded portion of the post you were replying to. The OP is looking to use a hydraulic cylinder as an air cylinder because they can get a hydraulic cylinder cheaper than an air cylinder.
Still air powered, just using a hydraulic cylinder with air in it vs an air cylinder with air in it.

Aaron Z

 

[Norm W]

Realize that using air is like using a giant spring. Hydraulic will stop when the flow stops. Air will push till the limit is hit. A buffer at the end if the stroke will help to limit the amount of stress caused by the ram hitting the end of it's stroke.

 

[SmallChange]

Just a thought from an industrial mechanical design viewpoint -- that sounds like an unsafe application for pneumatic actuation right from the start. Because air cylinders are springs, if you build up much force in trying to make a cut, and it suddenly breaks loose, there's an enormous release of energy. It's like adding a huge spring to a pry bar. When you pry something difficult, and it suddenly comes loose, you've got explosive mechanical action. Hydraulics have very little of this because there's not much compressibility.

We don't like big stored energies that can release suddenly, if they're not specifically required for the job.